Sallen-Key Low-pass Filter need help

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integralx2

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I am trying to understand what exactly Sallen-Key filters are. Now I understand they act as low pass filters. But whats the benefits of using this setup, over using a basic low pass filter ( resistor in parallel with capacitor)? I know that the Q factor will control how fast it rolls off. But, how does something like this effect signals in the 100-1k Hz range ? Thank you for the help
 

hi,
Download the free TI Filter Pro, its a filter calculator program.
Active Filter Design Application - FILTERPRO - TI Software Folder
 
The Sallen-Key is a specific type of ACTIVE filter that can be designed/configured as either lowpass, highpass or bandpass. The obvious advantage of an active filter over passive is the former is capable of gain and the latter is not. You can read up on the particulars here:

Sallen

EDIT: I see Mr Gibbs posted, while I was writting... Yes, FilterPro is a very useful tool.
 
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The OP is also missing the concept of the "number of poles". A single RC is capable of only a "single pole", while active filters (be they SallenKey or not) are capable of implementing filters with many poles. The number of poles primarily determines the slope of how rapidly the filter rolls off beyond the cuttoff frequency.
 
To expand on Mike ML's comments, the number of poles determines the steepness of the rolloff and the required rolloff is determined by your application. For typical audio filter applications (cross-over networks, etc.) a 2-pole filter is often adequate. For signal processing applications a steeper rolloff and more poles may be required.
 
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